This invention relates generally to ink jet printing devices. In particular, the present invention is an ink container having an ink reservoir fluidically coupled to an ink outlet. The ink reservoir is defined by a first capillary member positioned adjacent the ink outlet and a second capillary member spaced from the ink outlet by the first capillary member. The first capillary member has a high resistance to the flow of ink while the second capillary member has a low resistance to the flow of ink. An ink level sensing feature positioned adjacent the interface of the first and second capillary members provides a reliable and accurate indication of a low ink condition in the ink reservoir of the ink container.
Ink jet printing systems frequently make use of an ink jet printhead mounted within a carriage that is moved back and forth across print media, such as paper. As the printhead is moved across the print media, a control system activates the printhead to deposit or eject ink droplets onto the print media to form images and text. Ink is provided to the printhead by a supply of ink that is either carried by the carriage or mounted to the printing system such that the supply of ink does not move with the carriage. For the case where the ink supply is not carried with the carriage, the ink supply can be in fluid communication with the printhead to replenish the printhead or the printhead can be intermittently connected with the ink supply by positioning the printhead proximate to a filling station to which the ink supply is connected whereupon the printhead is replenished with ink from the refilling station.
For the case where the ink supply is carried with the carriage, the ink supply may be integral with the printhead whereupon the entire printhead and ink supply is replaced when ink is exhausted. Alternatively, the ink supply can be carried with the carriage and be separately replaceable from the printhead or drop ejection portion.
Regardless of where the supply of ink is located within the printing system, it is critical that the printhead be prevented from operating when the supply of ink is exhausted. Operation of the printhead once the supply of ink is exhausted results in poor print quality, printhead reliability problems, and, if operated for a sufficiently long time without a supply of ink, can cause catastrophic failure of the printhead. This catastrophic failure results in permanent damage to the printhead. Therefore, it is important that the printing system be capable of reliably identifying a condition in which the ink supply is nearly or completely exhausted. In addition, the identification of the condition of a nearly or completely exhausted ink supply should be accurate, reliable, and relatively low cost, thereby tending to reduce the cost of the ink supply and the printing system.
One type of ink container including a capillary reservoir with a binary ink level sensor is disclosed in the U.S. Pat. No. 5,079,570 to Mohr et al. entitled xe2x80x9cCapillary Reservoir Binary Ink Level Sensorxe2x80x9d which is assigned to the same assignee as the instant application and which is incorporated herein in its entirety by reference thereto. As illustrated in prior art FIG. 2 of the instant application, Mohr et al. is directed to an ink container 10 that includes a housing 12 within which is provided a capillary reservoir 14 for storing a quantity of ink. In prior art FIG. 2, the capillary reservoir 14 has dashed horizontal lines where there is ink and no dashed horizontal lines where there is no ink. On one end of the housing 12 is an ink outlet 16.
An ink level sensor 18 is provided on one surface of the housing 12. The sensor 18 comprises a C-shaped, transparent, ink level sensing tube 20 with first arm or port 20a a first distance above the outlet 16 and a second arm or port 20b a shorter distance above the outlet 16. Both the first and second ports 20a, 20b are ported through the housing 12 to the capillary reservoir 14. In operation, as long as the ink level 22 is above the first port 20a, the tube 20 of the ink level sensor 18 is full of ink and is in static equilibrium. However, when the ink level 22 reaches the top port 20a, the ink is sucked from the tube 20 of the ink level sensor 18 and into the capillary reservoir 14 due to an imbalance in the capillary pressures at the ink/air interfaces between the capillary reservoir 14 and the top port 20a. The resulting sudden (i.e., instantaneous) depletion of ink in the tube 20 of the ink level sensor 18 provides a binary fluidic indicator. Since the tube 20 of the ink level sensor 18 is transparent, a sensing device, such as light detector 24, positioned adjacent to the tube 20, can detect when the tube 20 is empty (i.e., detect the binary fluidic indicator), whereupon a printing system controller (not shown), coupled to the light detector 24 via transmission line 26, can notify a user of the low ink condition of the ink reservoir 14 of the ink container 10.
A drawback of the ink container 10 is that as ink is drained from the ink reservoir 14, the ink level 22, otherwise known as an ink front, since it forms a dividing line between an ink filled portion 28 of the ink reservoir 14 and an empty portion 30 of the reservoir 14, is very uneven and ever-changing. This uneven ink front 22 (i.e., ink level) exhibits an ink front variation 32 defined by the difference between a highest point 34 of the ink filled portion 28 of the ink reservoir 14 and a lowest point 36 of the empty portion 30 of the ink reservoir 14. This ink front variation 32 causes variation in the time at which the ink front 22 reaches the top port 20a of the ink level sensing tube 20 and the tube 20 drains. The greater the ink front variation 32 (i.e., unevenness), the greater the uncertainty in the amount of ink in the ink cartridge 10 at the time the ink level sensing tube 20 is drained. Moreover, because of this ink front variation 32, the time required for the ink front 22 to reach the ink level sensing tube 20 (i.e., the timing of the binary fluidic signal indicating a low ink condition for the ink container 10) can vary from one ink container 10 to the next. As such, it is relatively difficult for a printing system to precisely determine what the ink level is in any given ink container 10.
There is a need for an ink container that allows a printing system to reliably and accurately determine the ink level within an ink reservoir of the ink container. The ink container design should substantially eliminate the container-to-container variation in the indication of a low ink condition with an ink container. In other words, the binary fluidic signal for a low ink condition produced by an ink level sensor should occur in each and every container at substantially the same targeted ink level (i.e., with substantially the same amount of ink remaining in each and every ink container). Lastly, the ink container should be relatively easy and inexpensive to manufacture.
The present invention is a replaceable ink container for providing ink to a printhead of a printing system. The ink container has a fluid outlet configured for connection with the printhead. The ink container includes an ink reservoir having a first capillary member having a first capillary pressure, and a second capillary member having a second capillary pressure that is different than the first capillary pressure.
In one aspect of the present invention, the second capillary pressure is greater than the first capillary pressure such that the second capillary member has a higher resistance to ink flow than the first capillary member. In another aspect of the present invention, an ink level sensor senses a low ink condition of the ink reservoir. The ink level sensor includes a C-shaped tube mounted to the ink container. The C-shaped tube has first and second ports that fluidically communicate with only the second capillary member. The first and second capillary members abut one another at a capillary member interface, and the first port is positioned immediately adjacent to this capillary member interface. In a further aspect of the present invention, the C-shaped tube is transparent, and a light detector detects when the C-shaped tube is free of ink which defines the low ink condition of the ink reservoir. In still a further aspect of the present invention, the ink level sensor is a pressure sensor for sensing a change in back pressure within the ink reservoir at the capillary member interface.
In another embodiment, the present invention provides a replaceable ink container for providing ink to a printhead of a printing system. The ink container has a fluid outlet configured for connection with the printhead. The ink container includes an ink reservoir having a first capillary member, and a second capillary member that is different than the first capillary member. An ink level sensor determines an amount of ink in the ink reservoir.
In a further embodiment, the present invention provides a replaceable ink container for providing ink to a printhead of a printing system. The ink container has a fluid outlet configured for connection with the printhead. The ink container includes an ink reservoir having a first capillary member, and a second capillary member that is different than the first capillary member and is positioned immediately adjacent to the fluid outlet. The first capillary member is spaced from the fluid outlet by the second capillary member, and the first and second capillary members abut one another at a capillary member interface. An ink level sensor determines an amount of ink in the ink reservoir, with the ink level sensor being positioned immediately adjacent the capillary member interface so as to be in fluid communication with the ink reservoir.
In still a further embodiment, the present invention provides a replaceable ink container for providing ink to a printhead of a printing system. The ink container has a fluid outlet configured for connection with the printhead. The ink container includes an ink reservoir and an ink level pressure sensor. The ink level pressure sensor determines an amount of ink in the ink reservoir, with the ink level pressure sensor sensing a change in back pressure within the ink reservoir.
In still another embodiment, the present invention provides a replaceable ink container for providing ink to a printhead of a printing system. The ink container has a fluid outlet configured for connection with the printhead. The ink container includes an ink reservoir having at least one capillary member, and one additional capillary member. The one additional capillary member abuts the at least one capillary member at a capillary member interface, such that at the capillary member interface, the one additional capillary member has an ink level variation between an ink drained portion of the one additional capillary member and an ink filled portion of the one additional capillary member that is minimal.
This ink container allows a printing system to reliably and accurately determine the ink level within the ink reservoir of the ink container. In particular, by providing the ink reservoir with a second capillary member having a greater capillary pressure than a first capillary member of the ink reservoir, the ink within the ink reservoir will drain first from the first capillary member and then from the second reservoir. Placement of the ink level sensor immediately adjacent to the capillary member interface (or sensing a change in back pressure at this interface) between the first and second capillary members, with the ink level sensor in fluid communication with only the second capillary member, minimizes the ink level variation between an ink drained portion of the second capillary member and an ink filled portion of the second capillary member. By minimizing the ink level variation at the ink level sensor, the container-to-container variation in the indication of a low ink condition of an ink container is substantially eliminated. In other words, the binary fluidic signal for a low ink condition produced by an ink level sensor occurs in each and every container at substantially the same targeted ink level (i.e., with substantially the same amount of ink remaining in each and every ink container). Lastly, the ink container of the present invention is relatively easy and inexpensive to manufacture.